1. Field of the Invention
The present invention relates to an actuator for an inkjet print head, and more particularly, to an actuator for an inkjet print head, in which a chamber plate has hard etch stopper films formed at its upper and lower surfaces, respectively, and solution chamber walls arranged between solution chambers formed in the chamber plate have a thickness such that they have a smaller width at a middle portion than at a upper portion or a lower portion, thereby increasing a rigidity of the chamber plate and a bonding force of the chamber plate to a member being bonded thereto.
2. Description of the Prior Art
Generally, an inkjet printer is a kind of printer by which ink in the form of droplets is jetted out and printed onto a paper.
In such an inkjet printer, a printer head is a part on which a print quality and performance of the inkjet printer is dependent. The printer head, in the past, has employed the electrification or deflection mechanism of ink such that it is configured to require a high voltage. At present day, however, the printer head mainly uses a drop-on-demand (DOD) mechanism. Such DOD manner enables easier printing by jetting out droplets of a recording solution onto a paper under atmospheric pressure on demand.
The printer head in the inkjet printer has very various configurations depending on a driving means, but the recent printer head has configurations using a piezoelectric material, particularly oxide piezoelectric material. Among such configurations, a configuration illustrated in FIG. 1 is typically used.
As shown in FIG. 1, the inkjet printer head includes a nozzle plate 100, a reservoir plate 200, a channel plate 300, a restrictor plate 400, a chamber plate 500, and a vibrating plate 600, which are laminated in sequence. On the vibrating plate 600, there is laminated a microactuator 700 which consists of a plurality of patterned electrodes spaced apart from each other by a certain distance and a plurality of patterned oxide piezoelectric elements spaced apart from each other.
The nozzle plate 100, the reservoir plate 200, the channel plate 300, and the restrictor plate 400, which are placed below the chamber plate 500, each has a channel serving to introduce ink into a solution chamber formed on the chamber 500 or jet out ink from the solution chamber. These plates may be also partially omitted, if necessary, such that the channels of various configurations are obtained. That is to say, some of the plates may omitted, and the channels formed in the plates, thus, have various configurations, depending on an ink channel desired by a manufacturer.
Meanwhile, in the printer head including an oxide piezoelectric element as a driving means, the fabrication of the vibrating plate and the chamber plate is very critical. In other words, for an excellent performance of the printer head, the vibrating plate must have a mechanical rigidity sufficient to interlock with a driving means. Consequently, it is preferred that the vibrating plate is thinner and more uniform in thickness.
Furthermore, as the chamber plate is a part in which ink is temporarily stored, it must be sufficient in storage capacity of ink, and maintained at a stable state when introducing or jetting out ink.
For this reason, in fabricating the actuator of the inkjet printer head, there are some cases where the chamber plate is mechanically processed to form solution chambers therein. Recently, however, while the vibrating plate and the chamber plate are formed in such a manner that they are integrally coupled by a electroforming process, etc. with each other, the solution chambers in the chamber plate are formed using an etching process. This enables an increase in the rigidity of the vibrating plate, and also allows the solution chambers to be uniformly formed at the desired shape and size.
FIG. 2 is a cross-sectional view illustrating the formation of laminated plates used for an actuator in the printer head of FIG. 1. As illustrated in FIG. 2, a vibrating plate 810 and a chamber plate 820 are bonded to opposite surfaces of an etch stopper film 830 made of silver (Ag) or platinum (Pt), respectively. After that, the resulting structure is subjected to a photolithographic process on the surface of the chamber plate 820 opposite to the bonded etch stopper film to form solution chambers.
That is to say, as shown in FIG. 3, a photoresist film 840 is applied on one surface of the chamber plate 820 to a desired thickness, and the applied photoresist film 840 is exposed to light using a mask, developed, and then partially removed by a washing process to be patterned in a shape as shown in FIG. 4.
Portions of the chamber plate 820 exposed through the patterned photoresist film 840 generally have a width smaller than that of the respective solution chambers to be formed in the chamber plate 820. Where the exposed portions of the chamber plate 820 are impregnated with an etching solution as shown in FIG. 5, the chamber plate 820 is etched slowly to form the solution chambers 821. The etching solution used in the etching process etches the chamber plate 820 at a very high etching speed until the etching reaches the etch stopper film 830 by its self controlling-reaction property.
When etching vertically the chamber plate 820 until the etching solution reaches the etch stopper 830, the chamber plate 830 is also laterally etched to an etched degree similar with the vertically etched degree.
However, when the etching is vertically gradually diffused in a sequence indicated as hidden lines in FIG. 5 and reaches the etch stopper 830, the chamber plate 830 is more laterally etched in a portion adjacent to the photoresist film 840 than in a portion adjacent to the etch stopper 830. Consequently, a width of the solution chambers formed in the chamber plate is gradually larger toward the photoresist film 840.
By etching the chamber plate 820 according to the above mentioned process, the solution chambers 821 having a shape as in FIG. 6 are formed in the chamber plate 820. Then, the photoresist film 840 remaining on the upper portion of the chamber plate 840 is removed by washing again. Subsequently, on the vibrating plate 810, the electrodes 710 (see, FIG. 1) and the piezoelectric material 720 (see, FIG. 1) are formed on the vibrating plate 810 which is aligned vertically concentrically with the solution chambers 821. In this way, a print head is fabricated.
As the solution chambers so formed are shaped to have a width gradually larger from a portion on which the etch stopper 830 is laminated, solution chamber walls 822 partitioning the solution chambers are shaped to have a width gradually smaller from an end bonded to the etch stopper 830, toward the opposite end.
Meanwhile, to the end of the respective solution chamber walls 822, to which the etch stopper 830 is bonded, and to the opposite end, there is conventionally bonded a channel plate or restrictor plate, in which an ink channel for introducing ink into the solution chambers or ejecting ink from the ink chambers.
Accordingly, when the solution chamber walls 822 are formed such that their ends, to which the channel or restrictor plate is bonded, are smaller in width, as compared to that of their opposite ends, to which the etch stopper 830 is bonded, a bonding force of the solution chamber walls to the channel plate or the restrictor plate is poor, as compared with a bonding force to the etch stopper 830. This results in a reduction in the rigidity of the chamber plate 820, and makes the tightness between the solution chambers unstable.
Moreover, where the adjustment in an etching time for forming the solution chambers 821 is not accurately controlled, the chamber plate 820 is excessively etched at a portion adjacent to the photoresist film 840, while severely deforming open ends of the photoresist film 840, as shown FIG. 7. This makes a shape of the solution chambers nonuniform.
In other words, in order to make a shape of the solution chambers in the chamber plate uniform, a time for carrying out the etching needs to be controlled with accuracy. However, it is difficult to artificially control with accuracy a point of time when the etching is terminated.
In particular, difficulty in adjusting the etching time, and ununiformity in a shape of the solution chambers, lead to a variation in an ink introducing and ejecting performance of the solution chambers. This contributes to an unstable print state in the print head.
Therefore, an object of the invention is to solve the above mentioned problems and to provide an actuator for an inkjet print head, in which solution chamber walls partitioning solution chambers formed in a chamber plate have a width smaller at a middle portion than at an upper portion and a lower portion, such that the chamber plate has an increased bonding force to members bonded to thereto, thereby improving a rigidity of the chamber plate.
Moreover, another object of the present invention is to provide an actuator for an inkjet print head, in which a vibrating plate and a chamber plate are bonded by means of a first etch stopper to each other, and a second etch stopper is formed, by a photolithography process, integrally on the surface of the chamber plate opposite to the first etch stopper, such that uniform solution chambers are formed between the first and second etch stopper films by an etch process.
Still, another object of the present invention is to allow an etching process for the formation of solution chambers to be carried out more easily.
In accordance with the present invention, these objects are accomplished by providing an actuator for an inkjet print head comprising: a vibrating plate; a first etch stopper film laminated on one surface of the vibrating plate; a chamber plate laminated on the surface of the first etch stopper film opposite to the vibrating plate, the chamber plate having a plurality of solution chambers and a plurality of solution chamber walls partitioning the solution chambers, the solution chambers being formed on the chamber plate in such a manner that they have a width larger at a middle portion than at an upper portion and a lower portion and are vertically perforated, the solution chamber walls being formed on the chamber plate in such a manner that they have a width smaller at a middle portion than at an upper portion and a lower portion; and a second etch stopper film laminated on the surface of the chamber plate opposite to the first etch stopper film, the second etch stopper film including through-holes arranged while communicating vertically concentrically with the solution chambers and having a width smaller than that of the solution chambers.